1. Field of the Invention
This invention relates to a linear, actinic energy ray-curable resin having a photopolymerizable unsaturated group and a carboxyl group, and more particularly to a linear, alkali-soluble, and actinic energy ray-curable resin containing regularly repeating cyclohexane rings.
This invention further relates to an alkali-developable, photocurable and thermosetting resin composition using the actinic energy ray-curable resin mentioned above and a cured product thereof, and more particularly relates to a liquid, alkali-developable, photocurable and thermosetting resin composition which is suitable for use in various applications, particularly for use as permanent masks for printed circuit boards, interlaminar insulating layers for multi-layer circuit boards, and the like and capable of forming a cured film exhibiting low dielectric properties and excelling in adhesiveness, resistance to electroless plating, electrical properties, flexibility, resistance to moisture absorption, and resistance to PCT (pressure cooker test) by means of a procedure comprising the steps of irradiating a coating film of the composition with actinic energy rays, then developing the exposed film with a dilute aqueous alkaline solution, thereby forming an image on the film, and finally curing the film by irradiation with actinic energy rays and subsequent heating, or by heating and subsequent irradiation with actinic energy rays, or by heating and to a cured film-forming technology using the composition mentioned above.
2. Description of the Prior Art
At present, as a solder resist for part of the household grade printed circuit boards and for virtually all the industrial grade printed circuit boards, a liquid developing type solder resist which is irradiated with ultraviolet light and then developed to form an image and thereafter finally cured (finish curing) by heating or exposure to light is adopted from the viewpoint of ensuring highly accurate formation of circuits with high density. Further, with due respect to the problem of environmental safety, the liquid solder resist of the alkali developing type which implements development with a dilute aqueous alkali solution as a developer has come to play the leading role. As such alkali developing type solder resists using a dilute aqueous alkali solution, for example, published Japanese Patent Application, JP 61-243869A discloses a solder resist composition comprising a photosensitive resin obtained by addition of an acid anhydride to the reaction product of a novolak type epoxy compound with an unsaturated monobasic acid, a photopolymerization initiator, a diluent, and an epoxy compound, and JP 3-253093A discloses a solder resist composition comprising a photosensitive resin obtained by addition of an acid anhydride to the reaction product of a novolak type epoxy compound with an unsaturated monobasic acid, a photopolymerization initiator, a diluent, a vinyltriazine or a mixture of vinyltriazine with dicyandiamide, and a melamine resin.
Although some material systems are heretofore proposed as a solder resist as mentioned above, a solder resist composition using mainly a photosensitive resin obtained by causing a polybasic acid anhydride to react with a reaction product of the above-mentioned novolak type epoxy resin and an unsaturated monobasic acid as a photosensitive component is currently used in large quantities in the practical manufacture of printed circuit boards. Although such a photosensitive resin is excellent in photocuring properties and alkali-developability, it is hardly possible to say that the above-mentioned resin has reached a satisfactory level in respect of the balance between the photocuring properties and the flexibility. Moreover, this resin has the drawback of being easy to generate cracks by the thermal shock according to the use aimed at because it tends to cause shrinkage during curing and exhibits low elongation and poor toughness.
Further, in view of high densification of the printed circuit board to cope with the recent trend of electronic devices toward decreasing weight and size, the desirability of producing the solder resist having high performance has been finding growing recognition. Moreover, the IC packages using a printed circuit board having the solder resist applied thereto and a sealing resin are recently used instead of the IC packages called QFP (quad flat-pack package), SOP (small outline package), etc. which use a lead frame and a sealing resin. These new packages have such structure that metals such as ball-like solder are arranged in an area on one side of a printed circuit board having the solder resist applied thereto, the IC chips are directly connected thereto on the other side by wire bonding or through the medium of the bumps etc., and they are sealed by a sealing resin. They are called by mnemonic names, such as BGA (ball grid array) and CSP (chip scale package). These packages have more pins than other packages such as QFP of the same size, but are easier to miniaturize. Moreover, also in mounting the devices, they realize a low percent defective owing to the self-alignment effect of ball-like solder, and the introduction of these packages is advanced quickly.
In the printed circuit boards having the heretofore commercially available alkali development type solder resist, however, the PCT resistance which is the long-term reliability test of a package was inferior, which resulted in exfoliation of a solder resist film. Moreover, another matter which came into question is the so-called popcorn phenomenon, i.e. the phenomenon that the absorbed moisture boils within the package during re-flow of the package at the step of mounting of devices and cracks occur in the solder resist film and the circumference thereof inside the package. Such drawbacks in resistance to moisture absorption and long-term reliability are undesirable not only in the case of the above-mentioned mounting technology but also in the products for other uses, such as a solder resist of a usual printed circuit board, a solder resist to be used in the manufacture of a flexible printed circuit board, and interlaminar insulating layers of multi-layer circuit boards like a build-up board.